1. Field of the Invention
The present invention is directed to the field of treatment of biological tissues using high voltage pulses, and more specifically to a multi-electrode pulse delivery system for the treatment of biological tissues using high voltage pulses.
2. Background
Cancer is one of the leading causes of disease, being responsible for over half a million deaths in the United States each year. For example, breast cancer is the most common form of malignant disease among women in Western countries and, in the United States, is one of the most common causes of death among women between 40 and 55 years of age. The incidence of breast cancer is increasing, especially in older women, but the cause of this increase is unknown. Malignant melanoma is another form of cancer whose incidence is increasing at a frightening rate, at least sixfold in the United States since 1945, and is the single most deadly of all skin diseases. One of the most devastating aspects of cancer is the propensity of cells from malignant neoplasms to disseminate from their primary site to distant organs and develop into metastases. Despite advances in surgical treatment of primary neoplasms and aggressive therapies, many cancer patients die as a result of metastatic disease.
To treat such cancers, several cancer therapies have been developed that are based on the application of electric fields to a tumor containing malignant cancerous cells. Some of these therapies involve the use of radiofrequency or microwave devices to cause heating of the tumor to kill cancerous cells via hyperthermia. Other therapies use electrical pulses to permeabilize the cancerous cells in the tumor to allow the introduction of toxic drugs. In yet other therapies, short, high voltage electrical pulses can be used as a purely standalone cancer therapy that kills tumors and abnormal cells without hyperthermia or drugs.
Unfortunately, a typical tumor generally extends over an area that exceeds the area that can be efficiently and/or effectively treated covered using conventional electrical pulse treatment systems. Conventional systems typically rely on electrode devices that are either needles, which are inserted into the tissue, or pins, which are placed on top of the tissue. Needles generally allow electric fields to be formed at any depth, limited primarily by the length of the needles. In contrast, pins allow the electric field to penetrate only a limited depth of the tissues, determined by the extent of the fringe electric field.
In many conventional electrical pulse systems, a pair of electrodes is typically used to generate electric fields using voltage pulses. In operation, the electrodes are manually placed on or near the tissue to be treated. Thereafter, a voltage pulse is applied across the electrodes to form an electric field for providing treatment. However, a two electrode arrangement can effectively only cover an area or volume having a generally elliptical shape with boundaries for electroporation or nanoporation determined by the electrode distance (generally limited to between 0.5 cm and 1.0 cm) and the applied voltage. Although a larger gap or spacing can be provided, such an arrangement can require application of a higher voltage pulse to generate the necessary electric field and/or providing longer pulse durations at the electrodes to ensure that a therapeutic electric field intensity is provided to all tissues to be treated. Further, such a configuration will require higher voltage generators and additional cabling requirements, which can lead to an overall higher cost.
To provide for treatment of a larger area or volume, some conventional systems use a larger number of electrodes. In a typical configuration, one electrode is provided that is surrounded by other electrodes. An electric field is then generated by applying a voltage pulse between the center electrode and the surrounding electrodes. Although such an arrangement allows a larger area or volume to be treated, such a configuration has several drawbacks. First, to expand the treatment area, a power supply providing a higher current (i.e., a larger power) would be needed. Second, even when such power supplies are available, the area or volume that can be treated can also be limited by the maximum voltage per distance between electrodes. An alternative is to use multiple power supplies with the multiple electrodes. However, the use of multiple power supplies requires a greater amount of power and complexity for managing the multiple power supplies.